Dan Lawrence, no need to delete. Here's a X10 solution.
I am assuming that there is electricity although there are no phones.
You can use a UM506 set to continuous contact and using low voltage wire, run it to an alarm bell also low voltage.
In some cases you can run as much as 1000 feet of low voltage wire. You will have to test this out to find what your max will be. You only need to bury it about 3 inches. Also, do not pull it taunt (tight). leave it loose.
Some of these BELLS are quite large and quite
LOUD